Past Questions

A first-class brick, when immersed in water for 24 hours, should absorb water by weight not more than 20% of its dry weight as per standard brick quality requirements. Therefore, option (c) 20% is correct. The other options are incorrect because 15% is too strict for first-class bricks, while 25% and 30% exceed the permissible water absorption limit and indicate poorer quality bricks.

In limit state design of RC beams, the concrete stress block is parabolic-rectangular. At the level of the centroid of compression steel, the compressive stress in concrete is taken as 0.36 fck for the standard stress distribution used in design. Hence option (c) is correct. Why the others are incorrect: - 0.416 fck and 0.446 fck are not the standard code values for concrete stress at the centroid of compression steel. - 0.57 fck is the maximum design compressive stress in concrete at the extreme compression fiber, not at the level of compression steel.

Rapid hardening cement attains early strength mainly because it contains a higher proportion of tri-calcium silicate (C3S), which hydrates quickly and produces strength at early ages. It is also usually finer than ordinary Portland cement, but the principal reason for early strength gain is the higher C3S content. Gypsum is added only to control the setting time and does not contribute to early strength. Finer grinding helps increase the rate of hydration, but it is a secondary factor rather than the main cause. Tri-calcium aluminate (C3A) reacts very rapidly, but it mainly affects initial setting and heat of hydration, not the main early strength development.

Based on established principles in Mechanical Engineering, the correct and most appropriate choice is 'Parabola' (Option B).

For a fixed beam with a central point load, the fixed end moments depend on the relative flexural stiffness of the beam segments. If the moment of inertia of the middle half-length is reduced to half, that portion becomes less stiff, so it attracts less bending resistance. As a result, the end restraints must carry a smaller share of the load-induced moment, and the fixed end moments decrease. Why others are wrong: - a) Increase: Incorrect, because reducing stiffness in the middle reduces the beam’s ability to develop larger end moments. - c) Remain constant: Incorrect, because fixed end moments are not independent of stiffness distribution when the section is non-uniform. - d) Change their direction: Incorrect, because the loading pattern is unchanged; only the magnitude of the fixed end moments is affected, not their sign.

The correct answer is **b) Column analogy method**. This is a **force method** (also called the **flexibility method**) because it determines the redundant forces first and then uses compatibility conditions to solve the structure. Why the others are incorrect: - **a) Slope deflection method**: This is a **displacement method**, since it solves for joint rotations and translations. - **c) Moment distribution method**: This is also a **displacement method**, based on balancing end moments due to joint rotations. - **d) None of these**: Incorrect because **column analogy method** is indeed a force method.